This invention relates generally to vehicular transmissions and more particularly to apparatus for sensing the position of the manual valve of an automatic transmission which determines the transmissions"" mode at any given time.
It is conventional to provide a switch assembly to receive mechanical gear selection inputs from the driver of a vehicle through various linkages and output electrical signals to the transmission electronic control unit indicative of the gear selections. Such switch assemblies generally comprise either a rotary movable contact mechanism such as those shown in U.S. Pat. Nos. 5,525,768 and 5,440,087, assigned to the assignee of the present invention, or a linear movable contact mechanism such as that shown in U.S. Pat. No. 5,231,254, also assigned to the assignee of the present invention. The present invention relates to the latter type in which an actuator carrying a set of movable contacts is caused to slide back and forth in dependence upon the longitudinal movement of the manual valve of the transmission. The movable contacts are spring biased into engagement with a stationary contact board having contact segments arranged in a selected pattern so that an on/off output signal is obtained based on the longitudinal position of the manual valve.
Typically, the actuator is held in place by a housing and some type of cover with clearance provided between the actuator, on the one hand, and the housing and cover on the other hand to permit the actuator to move with the manual valve. However, erratic and inconsistent voltage output signals have resulted from unintentional motion of the actuator due to the degree of motion available to the actuator. Clearances between the actuator and the housing and cover allow the actuator to move in all six directions of motion. Longitudinal, lateral and vertical translation together with pitch, yaw and roll motion alter the movable contact projection onto the stationary contacts thereby intensifying voltage drop irregularities. Also, as a result of vibration, the actuator will move within the associated clearances with sudden impacts between the actuator and the surrounding wall. This causes the contact mechanism to jump or bounce resulting in open signals. In addition, a more detrimental mode of failure can result after prolong vibration, that of contact wear. Vibration exacerbates the rubbing action of contacts against each other thereby breaking material, removing plating, if present, and roughening the interface. This action has been found to increase contact resistance from 1 ohm to as much as 700 ohms or more.
It is an object of the present invention to provide a gear recognition switch system which overcomes the above noted prior art limitations. Another object of the invention is the provision of a linear type gear recognition switch system which is less sensitive to vibration. Yet another object of the invention is the provision of a gear recognition switch system of the type described which is reliable and one which has improved contact life.
Other objects, advantages and details of the switch apparatus of this invention appear in the following detailed description of the preferred embodiment of the invention.
Briefly, in accordance with the invention, an actuator of a vehicular transmission gear recognition switch system mounts movable contacts which are adapted to slide into and out of engagement with stationary contact segments mounted in an associated housing in dependence upon the movement of the manual valve of the transmission. The actuator comprises integral, flexible members arranged to eliminate clearance between the actuator and the housing in two of three mutually perpendicular directions, the third mutually perpendicular direction being that of the intended motion of the actuator. A pair of beams of selected cross sectional area, one on either side of a manual valve engaging yoke, are formed by respective isolation slots in the base wall of the actuator with a projection formed centrally on each beam. The projections are adapted to be received on a platform surface of the housing and the compliant action of the beams eliminates vertical clearance when the beams are loaded upon assembly of the apparatus. An additional beam is located in the base wall on one side of the actuator by an isolation slot and is provided with a projection extended laterally outwardly from the side and which cooperates with spaced projections extending laterally outwardly from an opposite side of the actuator and which, when inserted in an opening in the housing, loads the additional beam in the lateral direction thereby eliminating lateral clearance. Elimination of the clearance in the vertical and lateral directions, while allowing longitudinal motion in dependence upon the longitudinal position of the manual valve of the transmission, results in elimination of contact chatter and enhancement of contact life in the gear recognition switch.